Since players will be way less expansive due to the CPU limit, it will take a whole lot of time until Shard3 will be full. And it also solves all the "when does my subscription start"-confusion. Two birds with one stone!

This sounds like a good compromise. New steam players get to build up a pretty decent base and can actually compete on an even playing field, while retaining the ability to get a subscription if they feel like it.

Only problem is, it seems like cross-sharding your script would need to be made easier to avoid having shard3 impact profits too much (since if it's too hard to expand outside of shard3 due to cross-shard mechanics, players are less likely to expand and thus get a subscription).